In the case of a surface discharge type alternating current (AC) plasma display panel (PDP), a high voltage is periodically applied to a panel capacitance. Generally, a driving circuit for energy recovery is employed in a driving circuit for such a PDP. The energy recovery driving circuit is a circuit that increases system efficiency, reduces Electromagnetic Interference (EMI) noise and stably/effectively drives a PDP for a sustain period by recovering energy of a charged/discharged panel capacitance.
FIGS. 1 to 4 illustrate various conventional energy recovery driving circuits. In this case, third to sixth switches SW3 to SW6 are preferably switches (also called clamping switches) provided with backward body diodes and capable of high speed switching. In the conventional energy recovery driving circuits shown in FIGS. 1 to 3, first and third switches SW1 and SW3 are also preferably switches provided with backward body diodes. Further, a resonant inductor L is an unsaturated inductor, which is operated linearly within the range of a panel drive operating current.
In the drawings, a PDP is represented by an equivalent circuit modeled upon a parallel circuit that consists of a current source indicating discharge current and a capacitance C with a certain value. First, second, fifth and sixth diodes D1, D2, D5 and D6 represent high speed switching diodes.
In a first conventional circuit shown in FIG. 1, a first switch SW1 is turned on to allow an input voltage to be converted to a resonance voltage, thus charging the panel capacitance C through the resonant inductor L. In this case, the voltage of the panel capacitance C increases up to the input voltage by the resonance of the resonant inductor L connected in series with the panel capacitance C (because a voltage at the resonant inductor L, v=L (di/dt)), and, immediately after that, the third switch SW 3 is turned on to supply energy to the panel. When the panel capacitance C is discharged, the second switch SW2 is turned on to cause resonance, thus recovering voltage energy stored in the panel capacitance C to an input voltage source. In this case, the first conventional circuit is. disadvantageous in that, since the first switch SW1 must be compulsorily turned off when the voltage of the panel capacitance C becomes ½ of the input voltage (which is a voltage input to the panel during a sustain period, that is, sustain voltage), a control operation is complicated, and since a turn-off hard switching must be carried out when a maximum current flows through the switch, operating efficiency is deteriorated. Further, even at the time of energy recovery, since the second switch SW2 must be compulsorily turned off when a voltage between both ends of the panel capacitance C becomes ½ of the input voltage, a control operation is also complicated and operating efficiency is deteriorated. Further, when the panel is discharged, the turn-on control of the third switch SW3 must be accurately performed to smoothly supply energy to the panel.
In a second conventional circuit shown in FIG. 2, a very large capacitor voltage source or capacitor DC with a voltage of ½ of a panel input voltage is provided outside the circuit, and the resonance of a resonant inductor L connected in series with the panel capacitance C is used. A first switch SW1 is turned on to increase a voltage of the panel capacitance to the input voltage, and, immediately after that, the second switch SW3 is turned on to supply energy to the panel. Thereafter, the second switch SW2 is turned on to cause resonance, thus recovering voltage energy stored in the panel capacitance C to the capacitor voltage source DC. Since half-wave resonance is naturally finished by diodes D1 and D2 connected in series with the first and second switches SW1 and SW2, respectively, a zero voltage switching can be performed and a control operation is simplified, but the number of elements increases and the circuit is complicated. Further, since the voltage of the capacitor voltage source DC is actually maintained at a level less than ½ of the input voltage due to the loss of the circuit, a voltage between both ends of the panel capacitance C cannot increase up to the input voltage. That is, the energy recovery driving circuit is operated while the resonance energy of thereof is always insufficient due to system loss. In order to overcome this disadvantage, there is required a control operation of maintaining the voltage of the capacitor voltage source DC at a level greater than or equal to a certain value (less than or equal to a certain voltage when the panel capacitance C is discharged). Further, since high frequency pulse current flows through the capacitor voltage source DC, Equivalent Series Resistance (ESR) loss is also generated. A circuit identical with each of the first and second conventional circuits is symmetrically arranged on the opposite side of the panel, and acts as an inverter circuit during one period, thus performing repeated operations.
A third conventional circuit shown in FIG. 3 performs resonance using a resonant inductor L connected in parallel with a panel capacitance C. First and fourth switches SW1 and SW4 are turned on to supply energy to a panel, and are simultaneously turned off after the supply of energy is finished. At this time, if a fifth switch SW5 is turned on, a voltage between both ends of the panel capacitance C half-wave resonates from a positive input voltage to a negative input voltage, and the resonance is spontaneously stopped by a fifth diode D5.
At this time, the third and second switches SW3 and SW2 are turned on to supply energy to the panel from the opposite direction. In the same manner as the above process, a second switch SW6 is turned on to perform a next operation. The third conventional circuit is disadvantageous in that the voltage between both ends of the panel capacitance suddenly changes from a positive input voltage to a negative input voltage, and it cannot increase up to the input voltage due to system loss as in the case of the second conventional circuit.
In a fourth conventional circuit of FIG. 4, modified from the third conventional circuit, a panel is divided into PDP1 and PDP 2 and panel capacitances are allowed to resonate with resonant inductors L1 and L2 connected in series with the panel capacitances, respectively. Since different inductors are used at the rising and falling of the voltage, rising and falling timing can be controlled and the voltage does not change suddenly. However, the fourth conventional circuit is disadvantageous in that the circuit and the control operation thereof are excessively complicated, and the voltage between both ends of each panel capacitance cannot increase up to the input voltage due to system loss.
The first conventional circuit is disadvantageous in that loss is generated due to the hard-switching, and accurate turn-off control for switches is required. The second conventional circuit is disadvantageous in that a large capacitor operated as another voltage source must be provided outside the circuit, and the number of elements increases. Further, the first to fourth conventional circuits require the accurate turn-on control for the third switch SW3 so as to smoothly supply energy to the panel. Further, the third conventional circuit is disadvantageous in that it is difficult to control the sudden change of the voltage between both ends of the panel capacitance, and it is also difficult to smoothly supply energy to the panel through the first to fourth switches SW1 to SW4. The fourth conventional circuit is disadvantageous in that the circuit and the control operation thereof are excessively complicated, and the panel must be divided into two parts and driven. The second to fourth conventional circuits are disadvantageous in that the voltage between both ends of the panel capacitance cannot increase up to the input voltage due to system loss. Accordingly, the second to fourth conventional circuits are problematic in that they cannot guarantee 100% zero voltage switching of the inverter clamping switches SW3 and SW4 supplying discharging energy to the panel, and switching loss and EMI noise are generated.